The present invention relates to a lead-free balance weight, which is used to rotary balance a vehicle wheel of an automobile, motorcycle, truck or the like. Whilst in motion, an unbalanced rotating tire can cause vibration. This vibration is transferred through the steering mechanism to the driver, thus creating an uncomfortable driving condition. Further, such vibrations have an adverse effect on the performances of the automobile, such as excessive tire wear. Accordingly, it is very important to control the wheel balance. Present balance weights are made of lead and come in a variety of sizes so as to allow a desired weight to be positioned in the desired location of the wheel rim in order to obtain the correct balance.
Because, it is recognized that lead is toxic to the human body, it is undesirable to use lead from an environmental point of view. Some toxicity of the balance weight can be transferred to a city water system when such falls off the wheel and finds its way into the water drainage system along a road and eventually into a municipality's water supply.
It has been suggested to use balance weights made of iron in place of the present balance weights made of lead, see for example, U.S. Pat. No. 6,250,721. However, such balance weights made of iron have a drawback that their volume must increase by about 44% to provide a balance weight having the same weight because the specific gravity (7.86 g/cc) of iron is considerably smaller than the specific gravity (9-11 g/cc) of the common lead alloys. Moreover, whereas a wheel balance weight made of a lead alloy can be easily deformed, it is very difficult to appropriately change the shape of the balance weight made of iron at the time of attachment because iron is very hard. Accordingly, there arises a problem that such an iron balance weight cannot be properly positioned along the contour of the wheel as is desired.
U.S. Pat. No. 6,364,422 (Apr. 2, 2002), entitled Balance Weight for Vehicle Wheel, discloses and claims a balance weight for a vehicle wheel which utilizes a metal clip that includes a hook portion shaped to correspond to the edge of a wheel flange and a leg portion onto which is molded a body of tungsten powder dispersed in a styrene-based copolymer. Although this balance weight system does avoid the use of lead, it is generally necessary for the polymer to constitute about 40 volume percent of the wheel weight, and it requires a reasonably sophisticated injection molding process for manufacturing. Other metal clips for attaching wheel weights are shown in U.S. Pat. Nos. 5,733,016 and 5,228,754. Whereas ideally, the manufacture of a balance weight from molten tungsten might be preferred, tungsten cannot be reasonably melted and forged. As a result, it is generally necessary to provide high density tungsten bodies through a pressing and sintering process. Accordingly, it is not possible to manufacture balance weights in the manner done heretofore for making lead weights by pouring the molten material over a pre-formed clip. Accordingly, alternative manufacturing methods have been sought to provide a cost effective manner of utilizing a high density tungsten for a vehicle balance weight.